Between July 25 and September 9, 1983, 16 cases of invasive
group
C streptococcal infection were identified in northern New Mexico.
The
group C streptococcus was isolated from the blood of 15 patients
and
the pericardial fluid of one patient. The organism isolated from
14
of the patients has been identified as a group C B-hemolytic
streptococcus--species Streptococcus zooepidemicus; the species of
the
remaining two isolates have not yet been determined. Ages of the
16
patients ranged from 19 to 89 years (median 74); 10 were male. All
patients were Hispanic.

In general, the clinical syndrome was characterized by fever,
of the patients has been identified as a group C B-hemolytic
streptococcus--species Streptococcus zooepidemicus; the species of
the
remaining two isolates have not yet been determined. Ages of the
16
patients ranged from 19 to 89 years (median 74); 10 were male. All
patients were Hispanic.

In general, the clinical syndrome was characterized by fever,
chills, and vague constitutional symptoms. However, five patients
had
localized signs of infection, including pneumonia, endocarditis and
meningitis, pericarditis, and abdominal pain that led to a
cholecystectomy for one patient and an appendectomy for another
patient. Two patients with multiple underlying medical problems
died.

A case-control study was undertaken to identify possible risk
factors for contracting group C streptococcal infections. Patients
and controls were matched for age, sex, ethnicity, and neighborhood
of
residence. Some of the possible risk factors investigated included
underlying illnesses, immunosuppressive medications, animal
exposure,
group activities, restaurants visited, and food items consumed.
Initial questionnaires identified eating "queso blanco," a homemade
white cheese, as the only risk factor associated with illness (10
of
15 case patients versus 7 of 45 controls, p 0.001). During
subsequent discussions, four of the five patients who did not
report
in the case-control study that they had eaten the homemade cheese
later remembered that they had consumed the cheese before the onset
of
illness. Thus, only one patient did not recall having eaten the
cheese before becoming ill.

The sole source of the homemade cheese consumed by the patients
was an ungraded, small (seven cows), family dairy farm in northern
New
Mexico. At the farm, the cheese was made from raw cows' milk and
was
not subsequently aged. It was distributed to several stores in
northern New Mexico within 24-48 hours after preparation in the
family
kitchen. Milk samples from the cows and cheese samples from the
stores were obtained for microbiologic analysis. Group C
B-hemolytic
streptococci, species S. zooepidemicus, have been isolated from
multiple samples of each.

Editorial Note

Editorial Note: Group C streptococci are a common cause of
infection
in several animal species but are generally considered to be a rare
cause of infection in humans (1). Of the four species of group C
streptococci, S. equisimilis has been reported to cause most human
illnesses, including bacteremia, endocarditis, meningitis,
pneumonia,
epiglottitis, puerperal sepsis, and wound infections. However, S.
zooepidemicus has been associated with two outbreaks of pharyngitis
and nephritis in Europe (2,3). While pharyngitis was not a part of
the clinical syndrome in the outbreak reported here, it is too
early
to tell if poststreptococcal glomerulonephritis will develop.

In both of the European outbreaks, unpasteurized milk was
suspected as the source of infection. The outbreak reported here
is
the first epidemic of group C streptococcal infections in the
United
States and is the first such reported outbreak in which the
vehicle--cheese made from unpasteurized cows' milk--has been
epidemiologically implicated. Although S. zooepidemicus and S.
equisimilis are rarely reported causes of mastitis in cows, the
cause
of this outbreak was contaminated milk from cows with mammary
infections due to S. zooepidemicus.

Because few laboratories routinely determine the species of
group
C streptococci, the number of human infections due to S.
zooepidemicus
is not known. Furthermore, group C streptococci may be mistakenly
identified as group A strains if only bacitracin susceptibility
testing is done to differentiate group A streptococci from other
B-hemolytic streptococci. It is impractical for clinical
laboratories
to routinely determine the serogroup and species of all B-hemolytic
streptococci isolated from all sites. However, serogroups of
B-hemolytic streptococci and species of group C strains isolated
from
blood and other normally sterile sites should be identified if
further
information is to be gained about the epidemiology of such
infections.

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